The following studies will be initiated or continued during the grant period. 1) Further investigation of the relationship between white cell counts and death in Balb/c and C57 mice infected with Friend virus and subsequently treated with graded doses of vitamin B12 or a derivative. 2) Further studies to determine changes in B12 levels in tissues during viral injections and at different stages of the disease. 3) Studies on the isolation and synthesis of certain vitamin B12 derivatives. 4) Further studies on the changes in leukemic and normal leukocytes and bone marrow growth and maturation as influenced by B12 derivatives.